import math;

x1,y1,x2,y2 = map(float,input().split());

x = (x2 - x1)**2;
y = (y2 - y1)**2;

c = math.sqrt(x + y);
print('{:.8f}'.format(c));
 import math math x1,y1,x2,y2 = map(float,input().split()) x1 map(float,input().split()) map float input().split() ().split () input split y1 x2 y2 x = (x2 - x1)**2 x (x2 - x1)**2 x2 - x1 x2 x1 2 y = (y2 - y1)**2 y (y2 - y1)**2 y2 - y1 y2 y1 2 c = math.sqrt(x + y) c math.sqrt(x + y) math.sqrt math sqrt x + y x y print('{:.8f}'.format(c)) print '{:.8f}'.format(c) '{:.8f}'.format '{:.8f}' format c x2,y2 = map(float,input().split()) map(float,input().split()) x2 y1,x2,y2 = map(float,input().split()) map(float,input().split()) y1 x = (x2 - x1)**2 (x2 - x1)**2 x c = math.sqrt(x + y) math.sqrt(x + y) c y2 = map(float,input().split()) map(float,input().split()) y2 x1,y1,x2,y2 = map(float,input().split()) map(float,input().split()) x1 y = (y2 - y1)**2 (y2 - y1)**2 y
import math;

x1,y1,x2,y2 = map(float,input().split());

x = (x2 - x1)**2;
y = (y2 - y1)**2;

c = math.sqrt(x + y);
print('{:.8f}'.format(c));

